(1) Field of the Invention
The present invention relates to feeds containing docosahexaenoic acid and/or conjugated docosahexaenoic acid and a method for farming fish by using such feeds.
(2) Related Art Statement
Recently, the physiological activities of conjugated unsaturated fatty acids have been noted, which have been investigated by various organizations. For example, conjugated linoleic acid has been vigorously studied among the conjugated unsaturated fatty acids. More specifically, anticancer action, anti-arteriosclerosis action, antiallergic action, etc. are known as the physiological activities of conjugated linoleic acid.
However, although the physiological activities of conjugated linoleic acid have been actively studied, almost nothing is known about the physiological activities of conjugated unsaturated fatty acids other than conjugated linoleic acid.
Incidentally, farmed fishes contain more fat as compared with natural fishes, which degrades taste of the former. The excess accumulation of the fat is not preferable for the farmed fishes and consumers consuming such farmed fishes. In general, it is known that the composition of the lipid of the natural fish differs from that of the farmed fishes. With respect to the natural fishes, the lipid compositions depend upon the kinds of the fishes. There is a tendency that the content of the fat is smaller in the natural fishes than that of the farmed fishes and the content of triacylglycerol (TG) is also smaller in the former than in the latter. Differences in the lipid composition may influence the taste. Therefore, if the fat can be reduced and the lipid composition can be controlled by utilizing any physiological activity, high value-added farmed fishes can be preferably obtained without damaging the taste. However, a physiologically active material which reduces the fat and controls the lipid composition has not been known heretofore.
Under the circumstances, an object of the present invention is to provide a feed which can control the content of the fat and the lipid composition of the farmed fishes.
In order to accomplish the above object, the present inventor discovered that the body fat percentage and the lipid composition of the farmed fish can be controlled by adding docosahexaenoic acid and/or conjugated docosahexaenoic acid to a feed for the farmed fish.
The feed according to the present invention is characterized by comprising docosahexaenoic acid and/or conjugated docosahexaenoic acid.
In a preferred embodiment of the invention, the feed comprises 0.5% to 5% of docosahexaenoic acid and/or conjugated docosahexaenoic acid.
In another preferred embodiment, the structure of conjugated docosahexaenoic acid is at least one structure selected from a conjugated diene structure, a conjugated triene structure and a conjugated tetraene structure.
The present invention is also directed to a method for farming the fish by feeding it with any of the feeds mentioned above.
These and other objects, features and advantages of the invention will be apparent from the following description when taken in conjunction with the attached drawing, with the understanding that some modifications, variations and changes could be easily made with the skilled person in the art.